1. Field of the Invention
The present invention relates to impellers mounted to a rotary shaft, and more specifically to a centrifugal impeller.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A centrifugal impeller mount on a rotary shaft of the prior art is shown in FIG. 1. In this prior art arrangement, an interference fit is used to secure the impeller to the shaft by a tight fit. The shaft includes a smaller diameter portion 13 and a larger diameter portion 12. The impeller 14 includes a central hole having a larger diameter portion and a smaller diameter portion that forms a tight interference fit with the shafts, the interference fits occurring at locations 16 and 18 on FIG. 1. As the impeller spins, the fit loosens due to centrifugal forces. For heavily centrifugally loaded impellers, the fit has to be very large. This usually causes assembly and disassembly problems. Also, sometimes the impeller and shaft are of different materials and this too can cause problems with the fit. If the impeller has a higher coefficient of thermal expansion than does the shaft, at high temperatures the impeller will expand more than the shaft, and therefore the fit will loosen even more. When the centrifugal force from rotation is added, the fit will loosen even more. U.S. Pat. No. 6,481,970 B2 issued to Mukherjee et al on Nov. 19, 2002 and entitled COMPRESSOR WHEEL WITH PRESTRESSED HUB AND INTERFERENCE FIT INSERT is one prior art reference that shows this design.
It is therefore an object of the present invention to provide for an impeller mounted to a rotatable shaft with a fit that will not loosen during rotation.
It is another object of the present invention to provide for an impeller that can be mounted to the rotatable shaft without pre-stress such that the impeller can more easily be inserted onto the shaft.